1. Field of the Invention
This invention relates to a brush holder assembly for use in a dynamoelectric machine and more specifically to a brush holder assembly having an improved orientation of the assembly components to facilitate service.
2. Description of the Related Art
High speed large dynamoelectric machines utilize extremely high numbers of brush holder assemblies which frequently fully occupy all available circumferential space around a rotatable commutator or rotor of the machine. As is well known, each brush holder assembly includes a housing holding a plurality of individual carbon brushes mounted in stationary brush boxes. The carbon brushes are each biased into contact with the rotating commutator surface by a spring biasing mechanism. Each brush has a flexible shunt wire which is connected to the brush box to assure good electrical flow between the brush and a main electrical terminal that is carried by the brush holder housing.
The individual brushes are subject to constant wear and need to be periodically removed and replaced for which purpose suitable access must be provided. Providing access which allows for suitable working clearance has become very difficult because of the large number of brushes and their close relationship to each other. During brush replacement, the spring biasing mechanism must of course be removed, the shunt wire disconnected, and the brush removed. The new brush must be installed, the spring biasing mechanism reinstalled and the shunt wire reconnected.
In the prior art it is the practice to provide a single unitary housing containing a plurality of brush boxes. Brushes are subject to overheating which can damage or warp the brush box housing. If any part of the brush box housing is damaged, replacement of the entire housing is needed and this requires even more access than replacement of individual brushes. Replacing the entire unitary housing also increases the expense.
Prior art brush assemblies have not been ergonomically designed to permit service personnel to efficiently insert hands and tools in the limited space available. More specifically, the orientation of the individual components of the assembly have not facilitated either brush replacement or brush box housing replacement. Because the brush assemblies of dynamoelectric machines have not been ergonomically orientated, their installation has been cramped and access thereto for service and replacement has been awkward. This reduces safety and increases the hours required to service the machine. The hourly rate paid for such service is very high making such work extremely expensive. In addition, the dynamoelectric machine is out of production during this time which adds to the total cost of service.
The prior art discloses many arrangements for mounting brushes in a dynamoelectric machine including those described in the following patents: U.S. Pat. No. 4,246,507, Weldon et al; U.S. Pat. No. 4,329,611, Ohmstedt et al; U.S. Pat. No. 4,366,404, Ziegler; U.S. Pat. No. 4,602,181, Dietrich et al; and U.S. Pat. No. 4,663,552, Ohmstedt. All of these patents show brush holders with replaceable brushes wherein the various components are widely spaced apart in awkward locations making access difficult, time consuming, expensive and less safe. This prior art does not provide the various components in one location to concentrate the locus for service and replacement in the most compact area possible to maximize the accessibility provided by service openings in the machine. Further, this prior art does not deal with the problem of how to minimize time and cost when there is damage to the unitary brush housing requiring replacement.